The Relationship Among TSP, PM10, PM2.5, and Inorganic Constituents of Atmospheric Participate Matter at Multiple Canadian Locations

Abstract

The Canadian NAPS (National Air Pollution Surveillance) network has produced one of the largest and more geographically diverse databases of high quality atmospheric particle measurements in the world. A maximum of ten and a minimum of two years of data are available for 19 Canadian locations. These data were used to investigate relationships between collocated measurements of TSP, PM₁₀, PM_2.5, SO₄ ^2-, and other inorganic ions and elements at a variety of urban and rural locations. Amongst all locations and all 24-hour measurements, the 10th and 90th percentile TSP concentrations were 22 and 98 μg m-³, respectively. A majority of the PM₁₀ concentrations were below 47 μg m-³ and most of the PM_{2 5} concentrations across Canada were below 26 μg m-3 (90th percentiles). On average across all sites, PM₂₅ accounted for 49% of the PM₁₀, and PM₁₀ accounted for 44% of the TSP. However, there was considerable variability among sites, with the mean PM_2.5 to PM₁₀ ratio ranging from 0.36 to 0.65. This ratio also varied substantially from measurement to measurement, but at most sites a majority (>50%) of the ratios were within ±10% of the median value. PM₂.₅ concentrations tended to increase from summer to winter except at some of the eastern sites, particularly the rural locations, where sulfate was an important constituent. Coarse particles (2.5 μm < diameter < 10 μm) were found to exhibit the opposite seasonal pattern. Particle levels were highest at a high-density traffic site in Montreal, Quebec. Excluding this site, which was influenced by local sources, the particle levels tended to be highest in southwestern Ontario. Depending upon site, only about 37% to 61% of the PM_2.5 could be explained given the measured concentrations of several inorganic ions and elements. Much of the unexplained portions are assumed to be carbonaceous and predominantly organic in nature. Due to the predominance of crustal material, a greater portion of the coarse particle mass (∼70%) was explained by the inorganic constituents.